A simple, rapid microcolumn preconcentration and separation technique is described for the determination of the trace rare earth elements Sm, Tm, Ho, and Nd in geological samples by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The technique was based on adsorption of analytes on Nanometer-Size Titanium Dioxide (NSTD) packed in a microcolumn and separation from the matrix at pH = 7.0. Quantitative adsorption of more than 94% of analytes was obtained in this work. The dynamic adsorption capacities of NSTD were found to be 14.59, 12.86, 14.38, and 15.58 mg g -1 for Tm, Sm, Ho, and Nd, respectively. The analytes were recovered quantitatively from NSTD with 2.0 mol L -1 HCl. The analytical procedure was optimized in terms of sample acidity, elution, flow rate of sampling, and sample volume. At a flow rate of 1.0 mL min -1 , the detection limits (3r) of the technique for Tm, Sm, Ho, and Nd with an enrichment factor of 50 were 0.06, 0.18, 0.08, and 0.1 ng mL -1, and the RSD were 1.8%, 4.7%, 2.0%, and 1.6%, respectively .